1. Field of the Invention
The present invention relates to a spiral wound type separation membrane element employed for a spiral wound type separation membrane module.
2. Description of the Prior Art
A membrane separation technique is used for various applications such as desalination of seawater or demineralization of brackish water for coping with water shortage, preparation of ultrapure water in the electronic industry and the medicinal field, recycling of waste water and separation, purification and concentration in the fields of food, medicine and fine chemical.
For example, a reverse osmosis membrane separation apparatus, an ultrafiltration apparatus, a microfiltration apparatus or the like is employed for membrane separation. Such a membrane separation apparatus utilizes a spiral wound type separation membrane module, which is excellent in pressure resistance and can be manufactured at a relatively low cost. In general, the spiral wound type separation membrane module is formed by a pressure vessel storing a spiral wound type separation membrane element having a separation membrane such as a reverse osmosis membrane, an ultrafiltration membrane or a microfiltration membrane.
FIG. 6 is a typical partially fragmented perspective view showing an exemplary conventional spiral wound type separation membrane element 100, and FIG. 7 is a typical sectional view along the axial direction of the spiral wound type separation membrane element 100 shown in FIG. 6.
As shown in FIG. 6, the spiral wound type separation membrane element 100 is formed by superposing separation membranes 22 on both surfaces of a permeated liquid passage forming member 30 and bonding three sides thereby defining an envelope-like membrane 40 having a three-layer structure, bonding an opening of the envelope-like membrane 40 to a water collection pipe 50 formed by a perforated hollow pipe and spirally winding the envelope-like membrane 40 around the outer peripheral surface of the water collection pipe 50 along with a raw liquid passage forming member 60.
In this case, each separation membrane 22 is prepared by supporting a membrane material on a nonwoven fabric member made of polyester fiber. Thus, the separation membrane 22 has mechanical strength.
The permeated liquid passage forming member 30 and the raw liquid passage forming member 60 are formed by netty substances made of polyester fiber.
As shown in FIG. 7, first and second anti-telescopic members 21a and 21b are mounted on both end surfaces of the wound envelope-like membrane 40 in the spiral wound type separation membrane element 100. The first and second anti-telescopic members 21a and 21b prevent the wound envelope-like membrane 40 from telescopically extending due to supply pressure for a raw liquid 7. The first anti-telescopic member 21a is formed with a hole receiving an end of the water collection pipe 50 and a raw liquid inlet 15. The second anti-telescopic member 21b is formed with a hole receiving another end of the water collection pipe 50 and a concentrated liquid outlet 16. The outer peripheral surface of the envelope-like membrane 40 is covered with a sheath member 20 made of glass fiber. The envelope-like membrane 40 and the sheath member 20 are bonded to each other with an adhesive.
As shown in FIGS. 6 and 7, the raw liquid 7 is supplied from the raw liquid inlet 15 of the first anti-telescopic member 21a. The supplied raw liquid 7 flows along the raw liquid passage forming member 60 on the outer side of the envelope-like membrane 40, and is discharged from the concentrated liquid outlet 16 of the second anti-telescopic member 21b as a concentrated liquid 9. On the other hand, a liquid permeated through the separation membranes 22 in the process of feeding the raw liquid 7 along the raw liquid passage forming member 60 flows into the water collection pipe 50 along the permeated liquid passage forming member 30, and is taken out from the other end of the water collection pipe 50 as a permeated liquid 8.
The spiral wound type separation membrane element 100 is mainly employed for desalination of seawater and brackish water. In this case, the water temperature of the supplied raw liquid 7, i.e., seawater or brackish water is not more than 40xc2x0 C. and the pH thereof is 2 to 10, generally around 7. In the spiral wound type separation membrane element 100, therefore, the nonwoven fabric members forming the separation membranes 2, the permeated liquid passage forming member 30 and the raw liquid passage forming member 60, all made of polyester fiber, are neither decomposed nor dissolved by the raw liquid 7, and the sheath member 20 made of glass fiber is neither decomposed nor dissolved by the raw liquid 7.
When the spiral wound type separation membrane element 100 is employed for process treatment in the field of food, medicine or fine chemical or waste liquid treatment following the process treatment, however, a high-concentration alkaline solution having a high water temperature and high pH is supplied as the raw liquid 7. Such an alkaline solution is basically an inorganic alkaline solution, and a general example thereof is aqueous NaOH.
In this case, the nonwoven fabric members forming the separation membranes 22, the permeated liquid passage forming member 30 and the raw liquid passage forming member 60, all made of polyester fiber as described above, are decomposed and dissolved by the alkaline solution having a high temperature and a high concentration beyond basic physical properties. Further, the sheath member 20 made of glass fiber is also decomposed and dissolved.
When supplying a high-concentration alkaline solution having a water temperature of at least 40xc2x0 C. and a pH value of 13 with no pressure or supplying a high-concentration alkaline solution having a water temperature of at least 60xc2x0 C. and a pH value of 11 in a state pressurized to at least 10 kgf/cm2, for example, the nonwoven fabric members forming the separation membranes 22, the permeated liquid passage forming member 30 and the raw liquid passage forming member 60 are deformed due to decomposition and dissolution. When the permeated liquid passage forming member 30 and the raw liquid passage forming member 60 are deformed, the permeated liquid passage and the raw liquid passage are blocked. Thus, the permeate flow rate of the spiral wound type separation membrane element 100 is remarkably reduced. Further, the separation membranes 22 lose mechanical strength due to deformation of the nonwoven fabric members serving as support members. Thus, the separation membranes 22 are broken to reduce membrane separability. In addition, it is conceivable that the deformed sheath member 20 cannot withstand pressure in high-pressure running and is broken due to reduction of strength. Thus, the spiral wound type separation membrane element 100 cannot provide sufficient membrane separability.
Also when the first and second anti-telescopic members 21a and 21b, the water collection pipe 50 and an adhesive (not shown) employed for assembling the spiral wound type separation membrane element 100 are decomposed and dissolved by the alkaline solution having a high temperature and a high concentration, the membrane separability of the spiral wound type separation membrane element 100 is reduced.
An object of the present invention is to provide a spiral wound type separation membrane element capable of treating an alkaline solution having a high temperature and a high concentration.
A spiral wound type separation membrane element according to an aspect of the present invention comprises a spiral wound type membrane component including a water collection pipe, a separation membrane having a nonwoven fabric member and a membrane material supported on the nonwoven fabric member and wound around the water collection pipe, a raw liquid passage forming member arranged on a surface of the separation membrane for forming a raw liquid passage and a permeated liquid passage forming member arranged on another surface of the separation membrane for forming a permeated liquid passage, and having an outer peripheral surface and an end surface, an end surface holding member holding the end surface of the spiral wound type membrane component, and an adhesive bonding at least two of the water collection pipe, the separation membrane, the raw liquid passage forming member, the permeated liquid passage forming member and the end surface holding member to each other, and the water collection pipe, the separation membrane, the raw liquid passage forming member, the permeated liquid passage forming member, the end surface holding member and the adhesive are made of heat-resistant alkali-resistant plastic.
In the spiral wound type separation membrane element, the water collection pipe, the separation membrane, the raw liquid passage forming member, the permeated liquid passage forming member, the end surface holding member and the adhesive are made of heat-resistant alkali-resistant plastic, whereby the members forming the aforementioned spiral wound type separation membrane element are neither decomposed nor dissolved also when an alkaline solution having a high temperature and a high concentration is supplied as a raw liquid. Therefore, the alkaline solution having a high temperature and a high concentration can be treated with the spiral wound type separation membrane element with stable performance.
In particular, the permeated liquid passage forming member and the raw liquid passage forming member are neither decomposed nor dissolved, whereby the permeated liquid passage and the raw liquid passage are not blocked. Therefore, the spiral wound type separation membrane element obtains a stable permeate flow rate. Further, the nonwoven fabric member supporting the separation membrane is neither decomposed nor dissolved, whereby the strength of the separation membrane is not reduced and the separation membrane is not damaged. Therefore, the spiral wound type separation membrane element attains stable membrane separability.
The spiral wound type separation membrane element may further comprise a sheath member covering the outer peripheral surface of the spiral wound type membrane component, and the sheath member may be made of heat-resistant alkali-resistant plastic. In this case, the sheath member made of heat-resistant alkali-resistant plastic is neither decomposed nor dissolved also when an alkaline solution having a high temperature and a high concentration is supplied as the raw liquid. Therefore, the strength of the sheath member is not reduced and the alkaline solution can be treated with stable performance also when the spiral wound type separation membrane element is run under high pressure.
The sheath member may include fibers, made of the heat-resistant alkali-resistant plastic, wound around the outer peripheral surface of the spiral wound type membrane component and the heat-resistant alkali-resistant plastic for embedding the fibers.
The sheath member may include a cylindrical netty substance, mounted on the outer peripheral surface of the spiral wound type membrane component, made of the heat-resistant alkali-resistant plastic. The sheath member may further include the heat-resistant alkali-resistant plastic for embedding the cylindrical netty substance.
The sheath member may include a planar netty substance, wound around the outer peripheral surface of the spiral wound type membrane component, made of the heat-resistant alkali-resistant plastic, and a member of the heat-resistant alkali-resistant plastic fixing a prescribed portion of the planar netty substance. The sheath member may further include the heat-resistant alkali-resistant plastic for embedding the planar netty substance.
The sheath member having the aforementioned structure is neither decomposed nor dissolved also when an alkaline solution having a high temperature and a high concentration is supplied as the raw liquid.
In the spiral wound type separation membrane element, the heat-resistant alkali-resistant plastic may include polyphenylene sulfide, polypropylene, polyphenylene oxide, polysulfone or epoxy resin. Such a material has heat resistance and alkaline resistance. Therefore, the members forming the spiral wound type separation membrane element made of the aforementioned material have heat resistance and alkali resistance.
In the spiral wound type separation membrane element, the permeated liquid passage forming member may include a netty substance formed by fibers made of the heat-resistant alkali-resistant plastic.
The netty substance is preferably arranged to guide a permeated liquid into the water collection pipe. Thus, the permeated liquid can be quickly guided into the water collection pipe, and permeation through the separation membrane is facilitated.
In the netty substance, the diameter of the fibers is preferably at least 0.1 mm and not more than 1 mm, and the distance between the fibers is preferably at least 0.1 mm and not more than 1 mm.
In this case, the resistance of the permeated liquid passage formed by the permeated liquid passage forming member can be reduced, while the charge density of the separation membrane in the spiral wound type separation membrane element can be increased to obtain a sufficient membrane area. Further, the shape of the fibers can be prevented from being transferred to the separation membrane by pressure applied in running, whereby the separation membrane is not damaged. Thus, a spiral wound type separation membrane element having high performance is implemented.
In the spiral wound type separation membrane element, the raw liquid passage forming member may include a netty substance formed by fibers made of the heat-resistant alkali-resistant plastic.
The netty substance is preferably so arranged that the raw liquid axially flows in the spiral wound type separation membrane element. Thus, the raw liquid can be quickly supplied, and permeation through the separation membrane is facilitated.
In the netty substance, the diameter of the fibers is preferably at least 0.1 mm and not more than 1.5 mm, and the distance between the fibers is preferably at least 1 mm and not more than 5 mm.
In this case, the resistance of the raw liquid passage formed by the raw liquid passage forming member can be reduced, while the charge density of the separation membrane in the spiral wound type separation membrane element can be increased to obtain a sufficient membrane area. Further, the shape of the fibers can be prevented from being transferred to the separation membrane by pressure applied in running, whereby the separation membrane is not damaged. Thus, a spiral wound type separation membrane element having high performance is implemented.
In a method of running a spiral wound type separation membrane element according to another aspect of the present invention, the spiral wound type separation membrane element comprises a spiral wound type membrane component including a water collection pipe, a separation membrane having a nonwoven fabric member and a membrane material supported on the nonwoven fabric member and wound around the water collection pipe, a raw liquid passage forming member arranged on a surface of the separation membrane for forming a raw liquid passage and a permeated liquid passage forming member arranged on another surface of the separation membrane for forming a permeated liquid passage, and having an outer peripheral surface and an end surface, an end surface holding member holding the end surface of the spiral wound type membrane component, and an adhesive bonding at least two of the water collection pipe, the separation membrane, the raw liquid passage forming member, the permeated liquid passage forming member and the end surface holding member to each other while the water collection pipe, the separation membrane, the raw liquid passage forming member, the permeated liquid passage forming member, the end surface holding member and the adhesive are made of heat-resistant alkali-resistant plastic, and the method of running a spiral wound type separation membrane element comprises steps of supplying an alkaline solution from an end of the spiral wound type separation membrane element as a raw liquid and taking out a permeated liquid from at least an end of the water collection pipe.
In the method of running a spiral wound type separation membrane element, the alkaline solution is supplied into the spiral wound type separation membrane element from an end thereof as the raw liquid. The raw liquid flows in the spiral wound type separation membrane element along the raw liquid passage forming member. Permeation takes place through the separation membrane in this process. The permeated liquid permeated through the separation membrane flows into the water collection pipe along the permeated liquid passage forming member, and is taken out from at least an end of the water collection pipe.
In the aforementioned spiral wound type separation membrane element, the water collection pipe, the separation membrane, the raw liquid passage forming member, the permeated liquid passage forming member, the end surface holding member and the adhesive are made of heat-resistant alkali-resistant plastic, whereby the members forming the spiral wound type separation membrane element are neither decomposed nor dissolved also when the alkaline solution is supplied as the raw liquid. Therefore, the an alkaline solution can be treated with the spiral wound type separation membrane element with stable performance.
In particular, the permeated liquid passage forming member and the raw liquid passage forming member are neither decomposed nor dissolved, whereby the permeated liquid passage and the raw liquid passage are not blocked. Therefore, a stable permeate flow rate can be obtained. Further, the nonwoven fabric member supporting the separation membrane is neither decomposed nor dissolved, whereby the strength of the separation membrane is not reduced and the separation membrane is not damaged. Therefore, stable membrane separability can be attained.
The pH of the alkaline solution may be at least 11. Further, the water temperature of the alkaline solution may be at least 40xc2x0 C. Also when supplying such an alkaline solution having a high temperature and a high concentration, treatment can be performed with stable performance.
In the aforementioned method of running a spiral wound type separation membrane element, the spiral wound type separation membrane element may further comprise a sheath member, made of heat-resistant alkali-resistant plastic, covering the outer peripheral surface of the spiral wound type membrane component, and the method of running a spiral wound type separation membrane element may further comprise a step of taking out a concentrated liquid from another end of the spiral wound type separation membrane element. In this case, the sheath member made of the heat-resistant alkali-resistant plastic is neither decomposed nor dissolved also when the alkaline solution is supplied as the raw liquid. Therefore, the strength of the sheath member is not reduced and the alkaline solution can be treated with stable performance also in high-pressure running. In particular, treatment can be made with stable performance also when an alkaline solution having a high temperature and a high concentration is supplied as the raw liquid.
In the method of running a spiral wound type separation membrane element, the raw liquid passage forming member may include a netty substance formed by fibers made of the heat-resistant alkali-resistant plastic, and the step of supplying the alkaline solution may include a step of feeding the alkaline solution in the axial direction of the spiral wound type separation membrane element along the netty substance.
Thus, the raw liquid is quickly supplied in the spiral wound type separation membrane element, and permeation through the separation membrane is facilitated.
The permeated liquid passage forming member may include a netty substance formed by fibers made of the heat-resistant alkali-resistant plastic, and the step of taking out the permeated liquid may include a step of guiding the permeated liquid into the water collection pipe along the netty substance.
Thus, the permeated liquid is quickly guided into the water collection pipe in the spiral wound type separation membrane element, and permeation through the separation membrane is facilitated.